Various network topologies exist for enabling terminal equipment at one node to communicate with terminal equipment at another node within the network. FIG. 1(A) illustrates a simple network comprised of a point-to-point connection between two pieces of terminal equipment T1 and T2. In this network, terminal T1 is able to send signals to T2 and can receive signals from T2. Similarly, terminal T2 can both transmit and receive signals from terminal T1. The link between terminals T1 and T2 may comprise a half duplex or full duplex line.
FIG. 1(B) is an example of an arbitrated loop connecting three or more terminals together in a network. In the arbitrated loop, terminal T1 sends signals to terminal T2, terminal T2 sends signals to terminal T3, terminal T3 sends signals to terminal T4, and terminal T4 sends signals to terminal T1. Thus, as shown in the diagram, terminal T1 receives signals from terminal T4, terminal T2 receives signals from terminal T1, terminal T3 receives signals from terminal T2, and terminal T4 receives signals from terminal T3. In essence, communication signals travel in one direction along the loop from a transmitting terminal T until it reaches a receiving terminal T. The terminals T in between do not process the signals but instead act as repeaters within the network. The arbitrated loop is an example of a ring network in which signals are passed from terminal to terminal until they reach the intended recipient or recipients.
FIG. 1(C) is an example of a network having a switch 10. According to this type of network, the switch 10 enables connectivity between a set of M terminals and a set of N terminals. Each of the terminals T1 to TM and T1 to TN may transmit, receive, or both transmit and receive signals. The switch 10 is typically a cross-over switch for making the necessary connections between any one of the terminals T1 to TM to any of the other terminals T1 to TN.
FIG. 1(D) is an illustration of a typical hub network, such as one for Ethernet. With this type of network, a number of terminals are connected to each hub 12. For instance, in this figure, terminal T(1)(1) to terminal T(1)(M) are connected to a common hub 12(1). Each of the terminals T(1)(1) to terminal T(1)(M) communicate with each other through the hub 12(1), which enables half duplex communication between the terminals. The hubs 12 may allow full duplex communication, in which case the hubs 12 may be considered switches. In either event, groups of terminals T communicate with each other through the hubs 12. The hubs 12 are interconnected to each other through a backbone 14 to enable terminals T associated with one hub to communicate with terminals T at another hub.
All of the networks can be considered to have an interconnect fabric. The interconnect fabric generally refers to the ability of a network to direct communication signals from a terminal T at one node to a terminal T at another node within the network. For the network shown in FIG. 1(A), the interconnect fabric may enable one of the terminals T to gain control of a common line which carries signals from either piece of terminal T to the other terminal T. For the network shown in FIG. 1(B), the interconnect fabric may involve some type of token sharing whereby one of the terminals T is able to transmit signals along the loop or ring. For the network shown in FIG. 1(C), the interconnect fabric refers to the switching of signals from one terminal T to another terminal T. For the network shown in FIG. 1(D), the interconnect fabric refers not only to the interconnection between terminals T at one hub 12 but also the interconnection between terminals T at different hubs 12.
Regardless of the network topology, the interconnect fabric also depends upon the communication protocol. One of the most common network protocols is the Ethernet, which is defined by IEEE Standard 802.3, which is incorporated herein by reference. Ethernet has evolved over the years and can be placed on different media. For example, thickwire can be used with 10Base5 networks, thin coax for 10Base2 networks, unshielded twisted pair for 10Base-T networks, and fibre optic for 10Base-FL, 100Base-FL, 1,000Base-FL, and 10,000Base-FL networks. The medium in part determines the maximum speed of the network, with a level 5 unshielded twisted pair supporting rates of up to 100 Mbps. Ethernet also supports different network topologies, including bus, star, point-to-point, and switched point-to-point configurations. The bus topology consists of nodes connected in series along a bus and can support 10Base5 or 10Base2 while a star or mixed star/bus topology can support 10Base-T, 10Base-FL, 100Base-FL, 1,000Base-FL, and Fast Ethernet.
Ethernet, as well as many other types of networks, is a shared medium and has rules for defining when nodes can send messages. With Ethernet, a node listens on the bus and, if it does not detect any message for a period of time, assumes that the bus is free and transmits its message. A major concern with Ethernet is ensuring that the message sent from any node is successfully received by the other nodes and does not collide with a message sent from another node. Each node must therefore listen on the bus for a collision between the message it sent and a message sent from another node and must be able to detect and recover from any such collision. A collision between message occurs rather frequently since two or more nodes may believe that the bus is free and begin transmitting. Collisions become more prevalent when the network has too many nodes contending for the bus and can dramatically slow the performance of the network.
Fibre Channel is another communications protocol that was designed to meet the ever increasing demand for high performance information transfer. As with Ethernet, Fibre Channel is able to run over various network topologies and can also be implemented on different media. For instance, Fibre Channel can work in a point-to-point network such as the one shown in FIG. 1(A), in an arbitrated loop such as the one shown in FIG. 1(B), and can also work in a cross-point switch configuration or hub network, such as those shown in FIGS. 1(C) and 1(D). Fibre Channel is essentially a combination of data communication through a channel and data communication through a network. A channel provides a direct or switched point-to-point connection whereas a network supports interaction among an aggregation of distributed nodes and typically has a high overhead. Fibre Channel allows for an active intelligent interconnection scheme, called a Fabric, to connect devices. A Fibre Channel port provides a simple point-to-point connection between itself and the Fabric.
For most networks, including those that operate under Ethernet and Fibre Channel, the digital interconnect fabric requires some examination of the signals in order to provide the desired interconnection. For instance, in sending signals from one terminal to another, the arbitrated loop, switch, or hub must examine the address in order to ensure that the signal is delivered to the desired terminal. This overhead associated with the digital interconnect fabric is a burden on the network and generally decreases efficiency, speed, and overall performance of the network.
Some attempts have been made to improve performance by using optical communication. By using optical signals and fibers, electromagnetic interference (EMI), noise, and cross-talk can be substantially eliminated and transmission speeds can be increased. Even with optical communication, however, the digital interconnect fabric typically involves converting these optical signals into electrical signals. For instance, with the arbitrated loop, each terminal T receives optical signals, converts them into electrical signals, reviews the addressing information within the electrical signals, and either processes those signals if that terminal T is the intended recipient or regenerates optical signals and forwards them to the next terminal T in the loop. For the network shown in FIG. 1(C), the switch 10 typically converts the optical signals into electrical signals in order to provide the desired interconnection between the terminals T. For the same reason, the hubs 12 also convert the optical signals from the terminals T into electrical signals in order to provide the proper routing to the desired destination terminal T. While the optical lines shield the signals from noise, cross-talk, and EMI, the need to convert the optical signals into electrical signals and then once again generate optical signals reduces signal quality, adds a layer of complexity and cost, and degrades the overall potential performance of the networks.